The present invention relates generally to rotary machines, and more particularly to actuated seals for rotary machines such as steam and gas turbines.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, a gas path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
It is known in the art of steam turbines to position, singly or in combination, variable clearance labyrinth-seal segments and brush seals in a circumferential array between the rotor of the turbine and the circumferentially surrounding casing to minimize steam-path leakage. Springs hold the segments radially inward against surfaces on the casing that establish radial clearance between seal and rotor but allow segments to move radially outward in the event of rotor contact. While labyrinth seals, singly or in combination with brush seals, have proved to be quite reliable, labyrinth seal performance degrades over time as a result of transient events in which the stationary and rotating components interfere, rubbing the labyrinth teeth into a xe2x80x9cmushroomxe2x80x9d profile and opening the seal clearance.
Accordingly, there is a need in the art for a rotary machine having improved leakage control between stationary and rotating components.
One embodiment of the present invention provides a seal assembly for turbomachinery for controlling flow of a fluid medium in a fluid path comprising a casing having an internal pressure load path and a seal carrier chamber. A movable seal carrier is disposed within the seal carrier chamber and interposed between the pressure load path and an external flow path. In addition, a pressure selecting apparatus is coupled to the pressure load path to control flow therethrough. Moreover, the position of the movable seal carrier moves in response to a pressure differential determined by the pressure selecting apparatus between the pressure load path and the external flow path.